A display device that includes a non-self-emissive display panel such as a transmissive liquid crystal display panel generally includes a light source device that is disposed behind the display panel (also referred to as a “backlight device”). The light source device included in the display device is capable of illuminating the back side of the display panel with light. When the back side of the display panel is illuminated with the light emitted from the light source device, an image is displayed visible on the front side of the display panel.
Examples of the light source device that is used in the display device include a direct light source device and a side-edge light source device. Among them, a generally-used type of direct light source device includes a chassis having the shape of a tray of low height, alight source such as a fluorescent tube, optical members having a sheet or plate shape (also referred to as optical sheets) that are arranged to control the properties of light transmitted therethrough, and a frame having a substantially square shape with an opening. In the light source device, the light source is disposed in front of the chassis, and the optical members are disposed in front of the chassis and the light source. The frame is attached to the front side of the chassis so as to cover a border portion of the optical members while the light source and the optical members are disposed in front of the chassis. Thus, the border portion of the optical members is sandwiched between the front side of a border portion of the chassis and the back side of the frame, whereby the optical members are held in the light source device. The light source device having the configuration described above is arranged to control the properties of the light emitted from the light source with the use of the optical members, and to illuminate the back side of the display panel with the light the optical members transmit.
The display device including the light source device described above includes a bezel having a substantially square shape with an opening (i.e., a frame shape), and the display panel. In the display device, the display panel is disposed in front of the light source device (to be specific, a border portion of the display panel is disposed in front of the frame of the light source device). The bezel is attached to the front side of the display panel and the light source device so as to cover the border portion of the display panel and the front side and lateral sides of the frame of the light source device. In the display device having the configuration described above, the border portion of the display panel is sandwiched between the front side of the frame of the light source device and the back side of the bezel, whereby the display panel is held in the display device.
In the display device described above, the display panel is disposed in front of the optical members. If the display panel is disposed close to the optical members, there could arise problems as follows. When the optical members are shifted due to vibrations of the display device that is caused by an external force applied thereto, the optical members and the back side of the display panel could get in contact with and rub against each other, resulting in scratches on the optical members and a polarizing plate that is affixed on the display panel. The scratches made on the optical members and the polarizing plate could change the state of light the optical members and the polarizing plate transmit, which causes luminance unevenness to show up in an image displayed on the display panel.
In addition, if the optical members change in size (especially if the optical members increase in size) due to a change in temperature or humidity, a wrinkle could occur in the optical members. Due to the wrinkle in the optical members, intensity distribution in a plane direction of the light emitted from the light source device does not become even, which causes intensity unevenness in the emitted light. Because the display panel is disposed close to the optical members, the back side of the display panel is directly illuminated with the light with uneven intensity (the intensity unevenness of the light is not lessened nor removed), which could cause luminance unevenness to show up in an image displayed on the display panel.
Thus, if the display panel is disposed close to the optical members, the luminance unevenness showing up in the image displayed on the display panel could lower the display quality of the display device. In order to solve this problem, the distance between the front side of the optical members and the back side of the display panel may be increased. However, the increase of distance between the front side of the optical members and the back side of the display panel causes a problem as follows.
If the distance between the optical members and the display panel is increased, the border portion of the optical members and a cushioning material for holding the border portion of the optical members are seen through the clearance between the optical members and the display panel when the display panel of the display device is seen from the front side. The border portion of the optical members, which is placed on the front side of the border portion of the chassis, and of which the back side is accordingly not illuminated with the light the light source emits, is darker than the other portion of the optical members that is illuminated with the light. For the same reason, the cushioning material for holding the border portion of the optical members is darker than the other portion. Thus, the border portion of the display panel looks darker than the center portion of the display panel, which causes a luminance difference between the border portion and the center portion of the display panel to lower the display quality of the display device.
In order that the border portion of the optical members and the cushioning material for holding the border portion of the optical members may not be seen when the display panel is seen from the front side, the border portion of the optical members and the cushioning material are preferably disposed so as to coincide outside inner peripheral edges of the opening of the bezel. To be specific, a region of the optical members that is capable of transmitting the light emitted from the light source device is increased, and the outline of the region is disposed so as to coincide outside the inner peripheral edges of the opening of the bezel. Thus, when the display panel is seen from the front side, the border portion of the optical members and the cushioning material are hidden from view behind the bezel, and only the region of the optical members that is capable of transmitting the light emitted from the light source device can be seen. Consequently, the border portion of the display panel has no portion having a low luminosity, whereby the luminosity of the display panel can be made even all over the panel.
However, in the configuration described above, structural objects provided to the chassis that are used to place the border portion of the optical members thereon or to maintain the strength of the chassis need to be disposed so as to coincide outside the inner peripheral edges of the opening of the bezel. Thus, the overall size of the chassis needs to be increased while the size of the opening of the bezel is unchanged, which increases the size of a so-called frame region of the display device. This configuration of the display device cannot be easily applied to a display device prepared in attempt to have a narrower frame region. Meanwhile, if the region of the optical members that is capable of transmitting the light is increased while the overall size of the chassis is not increased, a region of the chassis where the structural objects to maintain the strength of the chassis are provided becomes narrow. Thus, the structural objects to maintain the strength of the chassis need to be decreased in size, which could weaken the strength of the chassis.